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Question

Simplify: \(\frac{\sin A}{1-\cos A} + \frac{1-\cos A}{\sin A}\)

This question was previously asked in
RRB ALP 2025 CBT 2 Wiremen Question Paper (28-Jul-2026) (Shift 2)
The correct answer is

$2\cosec A$

Simplify Trigonometric Expression

The task is to simplify the following trigonometric expression:

\( \frac{\sin A}{1-\cos A} + \frac{1-\cos A}{\sin A} \)

Step-by-Step Simplification

  1. Identify the common denominator for the two fractions, which is \((1-cos A)sin A\).

  2. Rewrite the expression with the common denominator:

    \( \frac{\sin^2 A}{(1-\cos A)\sin A} + \frac{(1-\cos A)^2}{\sin A (1-\cos A)} \)
  3. Combine the numerators over the common denominator:

    \( \frac{\sin^2 A + (1-\cos A)^2}{(1-\cos A)\sin A} \)
  4. Expand the squared term in the numerator: $(1-cos A)2 = 1 - 2cos A + cos2 A$.

    \( \frac{\sin^2 A + 1 - 2\cos A + \cos^2 A}{(1-\cos A)\sin A} \)
  5. Use the Pythagorean identity $sin2 A + cos2 A = 1$.

    Substitute \(1\) for $sin2 A + cos2 A$:

    \( \frac{1 + (1 - 2\cos A)}{(1-\cos A)\sin A} \)
  6. Simplify the numerator:

    \( \frac{2 - 2\cos A}{(1-\cos A)\sin A} \)
  7. Factor out \(2\) from the numerator:

    \( \frac{2(1 - \cos A)}{(1-\cos A)\sin A} \)
  8. Cancel the common factor \((1 - cos A)\), assuming \( A \neq 2n\pi \):

    \( \frac{2}{\sin A} \)
  9. Apply the reciprocal identity \(cosec A = 1/sin A\):

    \( 2\cosec A \)

Final Result

The simplified expression is \(2\cosec A\).

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